Fasting has been practiced for centuries, and has been popularised as a diet trend over the last few years, with celebrity advocates including, Benedict Cumberbatch and Hugh Jackman. But can it really help you lose weight and get healthier?

What is Intermittent fasting?

Intermittent fasting is a term used for eating patterns that cycle between a fasting and non-fasting period. During the fasting period, you either severely restrict your calorie intake, or don't consume any food at all. The emphasis is on when foods are eaten, and there are several variations to this type of eating regime. Some of the recent popular trends have included:

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1. Intermittent energy restriction (IER)

The 5:2 diet: Made popular by TV doctor Michael Mosley, this plan involves eating approximately 600kcal on two days of the week and then eating regularly on the other five days.

The 6:1 Diet: This involves either consuming a low-calorie diet for one day of the week, or completely fasting for 24 hours, followed by six days of eating regularly.

3. Alternative day fasting (ADF)

Eat food every other day: In this plan 'fast' days where individuals consume <25% of baseline energy needs (approximately 500kcal) are alternated with 'feast' days where regular food consumption is permitted.

4. Periodic fasting (PF)

Eat-stop-eat diet: Once or twice a week individuals do a 24 hour fast (e.g. fast from 6pm one day to 6pm the next day) and then eat regularly on the other days.

However, whilst these findings are very promising, Junee stresses that more large scale clinical trials on humans are needed to assess the longer-term effects (e.g. over a year) of intermittent fasting, to really understand its true benefits and to enable clinical recommendations to be made. There is also not yet enough evidence to determine which 'variation' of fasting may be most effective plan for these health outcomes.

Does it work for weight loss?

Intermittent fasting can be an effective method of short-term weight loss. "A recent scientific statement from the American Heart Association (2017) reports that there is evidence that both alternate day fasting and periodic fasting may be effective for weight loss," explains Junee. "Changes in body weight from alternative day fasting and periodic fasting showed a 3-8% body weight decrease in all studies after 3 to 24 weeks."

However, what's lacking is data to show that this weight loss can be sustained in the long-term. The nature of fasting means that long-term compliance for most individuals is likely to be difficult. Beyond not knowing whether fasting will help keep the weight off for good, there are also some other potential pitfalls for using this approach to shed those extra pounds.

The downsides of fasting

1. It focuses on when to eat, not what to eat

Emphasis tends to be on calorie-counting rather than nutrition. "For this eating pattern to work it's really important that on the 'feasting' days, the foods chosen are packed full of nutrients i.e. plenty of fruit and vegetables, wholegrains, pulses, low fat dairy and lean protein foods," says Junee. "Eating foods high in fat and sugar like cakes, biscuits, chocolate, fried foods and sugary drinks may result in people not gaining the benefits from the fasting days."

Eating is very much a social activity, and being restricted to only eat in certain time windows may heavily impact on an individual's ability to attend social events and join others in normal mealtimes, etc.

4. Not suitable for all

"Fasting should not be recommended to pregnant women, young children, or anyone with a history of eating disorders as it has the potential to create an unhealthy obsession with food," says Junee.

It might have benefits, but it's not for everyone

People may choose to fast for various reasons be it health, religion or weight loss, and it may work for some. "In these cases, it's important for professionals to provide a tailored approachto these individuals based on any medical conditions they may have," recommends Junee.

"I practice a non-diet approach, and rather encourage people to recognise signals of hunger and fullness and to eat accordingly. Those looking to lose weight have often tried several diets and are still at square one – overweight and in poor health. What these clients often require is a little TLC, not another diet. I find the patients who learn to become intuitive eaters, and who practice a more mindful approach to eating, will often have better long-term outcomes with regards to improvements in health and weight loss."

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